1. Field
The present disclosure relates to the field of optical communication technologies, and in particular to a bias monitoring method and apparatus and a transmitter.
2. Description of the Related Art
In an optical transmitter, an optoelectronic modulator is used to modulate an inputted electric driving signal into an optical carrier and output an optical signal, with its operational principle being similar to that of a multiplier. In operation, the optoelectronic modulator needs to be applied direct current bias, so that it operates at a suitable direct current bias point. Therefore, a modulation feature of the optoelectronic modulator is related to a direct current bias point where it is located, and for a typical coherent optical communication system, an ideal direct current bias point of the optoelectronic modulator is at its half-wave transfer point.
In a long-haul optical communication system, a signal damage brought by deviation of a bias point of an optoelectronic modulator in a transmitter cannot be compensated for at a receiver side by a digital signal processor (DSP), thereby resulting in degradation of transmission performance. If the dynamic deviation of the bias point of the optoelectronic modulator is not tracked and corrected, said signal damage will become inherent damage to the system, and further affect the transmission quality along with the time.
In prior art, an LiNbO3 modulator for realizing high-speed optoelectronic transform usually needs to be introduced an automatic bias control (ABC) module at a receiver to dynamically track deviation of a bias point, so as to realize stable operation of the transmitter at relatively long time.
For typical application of an optoelectronic modulator in a communication system, that is, a direct current bias point is located at a half-wave transform point Vπ of the modulator, automatic bias control schemes discussed in Document 1 and Document 2 often use a manner of introducing scrambling frequencies on a basis of direct current bias, and use a method for sounding direct current optical power, a scrambling frequency linear term or a mixing term at an output end of a modulator to perform feedback closed-loop control on the direct current bias point.
In order to enhance sensitivity of a sounding signal to deviation of a bias point, Document 3 proposes an optical domain intra-variance sounding scheme based on a 3×3 coupler, in which sensitivity of a sounding signal is improved by using a self-coherent method.
Document 1: Pak S. Cho, et al., Photon. Technol. Lett. 18 (21), 2006;
Document 2: Li L., et al., J. Lightwave Technol. 28(11), 2010; and
Document 3: Liang D., Proc. OFC'20, OThT4, 2010.
It should be noted that the above description of the background is merely provided for clear and complete explanation of the present disclosure and for easy understanding by those skilled in the art. And it should not be understood that the above technical solution is known to those skilled in the art as it is described in the background of the present disclosure.